A multi-functional-group modified cellulose for enhanced heavy metal cadmium adsorption: Performance and quantum chemical mechanism

Heavy metal contamination directly threatened human life and health. In this work, a novel carboxyl, amide, carbonyl sulfide and secondary amino group grafted cellulose derivative adsorbent (modified-cellulose) was prepared in an attempt to remove heavy metal Cd2+. The XRD, FTIR, 13C NMR and XPS results showed that the carboxyl, amide, carbonyl sulfide and secondary amino group were grafted onto the cellulose backbone successfully. Effects of various factors on the adsorption performance were investigated as well as the adsorption mechanism. The Cd2+ adsorption capacity of modified-cellulose was pretty good, up to 401.1 mg/g and with 3 times enhancement. The adsorption process was spontaneous, well described by the Freundlich model (R2 = 0.994), confirmed to the pseudo-second-order model (R2 > 0.997), and mainly controlled by chemisorption. The density functional theory (DFT) calculations indicating that the Cd2+ binding ability of multi-functional groups modified cellulose was stronger than that of single-functional group modified cellulose. The preferential adsorption sites were analyzed based on the frontier orbital theory (FOT), and they were concentrated on the secondary amino groups and carbonyl sulfides. It is foreseeable that the as-prepared modified-cellulose adsorbent has great potential in heavy metal cadmium removal, and our conclusions could provide significant theoretical guidance in the due bioresource utilization.